The green algae belonging to the order Ulvales (Ulva sp. and Enteromorpha sp.) are present everywhere on Earth and are very commonly encountered on coasts. These algae are frequently involved in algal blooms promoted by eutrophication of coastal waters, giving rise to “green tides”.
Until now this undesirable biomass has been of very low added value and it is used essentially as compost.
The anionic complex polysaccharides present in the cell walls of the ulvales, called ulvans, possess unusual structures and represent a source of biopolymers whose functionalities have so far received little attention.
The ulvans are made up of various disaccharide repeating units constructed with rhamnose units, glucuronic acids, iduronic acids, xyloses and sulphates. The two main repeating units are called aldobiuronic acid, or ulvanobiuronic acids, or A (A3S) and B (B3S) respectively, which have the following formulae:

The A unit (A3S) is beta-D-1,4-glucuronic acid (1→4) alpha-L-1,4-rhamnose 3-sulphate. The B unit (B3S) is alpha-L-1,4-iduronic acid (1→4) alpha-L-1,4-rhamnose 3-sulphate.
The uronic acids are sometimes replaced with xylose residues sulphated to O-2.
The ulvans possess unique physicochemical properties that make them attractive candidates for new food-industry, pharmaceutical, and cosmetic applications. The ulvans possess very unusual structures composed of rare sugars or monosaccharides such as rhamnose and iduronic acid. Rhamnose is an important compound of the surface antigens of numerous microorganisms that are recognized specifically by mammalian lectins. It is also used for the synthesis of flavouring materials. Iduronic acid is used for the synthesis of glycosaminoglycans, for example heparin.
In addition to the monomers, the ulvans and oligo-ulvans have interesting biological properties. In fact, studies have shown, for example, that oligo-ulvans have antitumour, antiviral, notably anti-influenzal, and anticoagulant activities. A non-exhaustive list of potential applications of the ulvans was proposed by M. Lahaye and A. Robic in the document Structure and functional properties of ulvan, a polysaccharide from green seaweeds. Biomacromolecules 2007, 8, 1765-1774 [1].
In this context, better understanding of the structure of the ulvans and the development of methods for fragmenting the ulvans in oligomeric or monomeric form are of considerable interest.
At present, through lack of means for understanding them better and for degrading them efficiently, the algae, notably the green algae, are essentially composted, without any industrial utilization. This is all the more deplorable since it is an abundant source, which is sometimes troublesome in terms of pollution of our maritime coastlines. At present they are eliminated of by composting.
There is therefore a real need to find novel means of degradation of ulvans so as to be able to valorize this bioresource, obtained notably from green algae, producing “tailor-made” oligo-ulvan fragments in view of cosmetic, food-processing and medical applications.